Condenser device



H. GONNINGEN 2,315,199

March 30, 1943.

CONDENSER DEVICE Filed Feb. 11, 1939 fire/2i: Hermann cio'hnir m Patented Mar. 30, 1943 UNITED STATES PATENT OFFICE CONDENSER DEVICE Hermann Gi'mningen, Berlin, Germany; vested in the Alien Property Custodian Application February 11, 1939. Serial No. 255,833

4 Claims.

This invention relates to condenser devices of the fixed or variable type having a solid dielectric. particularly of a ceramic substance.

It has been found in connection with condensers that very considerable stresses occur at the edges of the electrode plates due to the strong concentration of the electric lines of force and that these stresses become particularly harmful when the solid dielectric presents a high dielectric constant and when the condenser assembly is exposed to the air, that is, when the edg of the electrode is surrounded by a dielectric having a very low dielectric constant and low disruptive strength. This inconvenient field distribution gives rise to corona effects which may lead to flash-over from one to the other electrode in direct potential condensers. In the intention to overcome this difficulty the critical edge of the dielectric has been considerably enlarged so as to decrease the electric field at the edge of the electrode plate or plates. It has also been proposed in connection with alternating current condensers to coat the edge with a very thin layer of a material having a very high resistance 50 as to decrease the field due to the reduced conductivity of the plate. Attempts have also been made to impregnate the whole condenser with fat or oil or even to provide blind plates. However, all these expedients have not been able to remove the difliculties. The method of enlarging the dielectric considerably increases thespace requirements and is possible only in connection with artificial or synthetic materials, such as ceramic, but is impossible to apply to natural mica. The application of a highly resistive edge is useful only in connection with an alternating voltage but introduces severe additional losses. The impregnation with fat or oil suffers under the disadvantage that the lrnpregnant becomes disintegrated due to transient overload conditions and produces carbon compounds at the critical points so that surface leakage paths may be set up during the course of time. Also the provision of blind intermediate plates causes'the potential to be divided into a plurality of partial potentials and is unable to prevent the strong concentration of the lines of force at the edge of the plate. The use of enlarged edges inthe form of toroidal extensions partially reduces the possibilities for reliably cooling the condenser so that the efliciency becomes unnecessarily reduced. The edge effect is specifically disa lvantageous when the new ceramic materials are used as the solid dielectric since these substances present a dielectric constant equal to 4-0 to 80.

It is the object of my present invention to avoid the aforementionel difficulties. This is accomplished according to the present invention particularly in connection with ceramic substances to form the insulation so that its edge is gradually Germany February 12, 1938 bevelled toward its outer boundary. It is thus possible to completely eliminate the electric field at the edge and to cause the lines of force to remain approximately in parallel relation with one another. Due to the fact that the thickness of the intermediate layer of insulation having a high dielectric conductivity gradually decreases toward the edge and that the intermediate layer of air having a low dielectric conductivity gradually increases, the total capacitive resistance gradually becomes reduced so that the edge effect cannot occur at any point.

The invention will be more readily understood .from the following description taken in conjunction with the accompanying drawing, in which Fig. 1 shows a condenser in which the lines of force are indicated, Fig. 2 shows one embodiment according to the invention, Fig. 3 a modification of the embodiment shown in Fig. 2, Fig. 4 a further modification according tothe invention, Fig. 5 is a side view of a condenser assembly according to the invention, while Fig. 6 is a top view of the arrangements shown in Fig. 5.

Referring first to Fig. 1 there is shown a condenser having metallic plates a and an intermediate insulating member b having a very high dielectric constant. The lines of force shown in this figure represent the natural path thereof and that these lines of force flow'almost parallel to one another. The most critical point is indicated with c where there is a, long path for the lines of force in a material having a high dielectric constant and a very short path in the air of low dielectric constant. In cases that the intermediate insulating layer would be uniformly tapered to a point at the edge, brush discharge phenomena would at first be set up at this point. In order to obviate or considerably reduce this possibility it is proposed according to one feature of the present invention to form an insulation so as to first provide a step at right angles with respect. to the metallic plates as shown by din Fig. 2 and to cause the remainder of the thickness to be gradually tapered down to form a point e at the edge.

A stlll'more convenient possibility is shown in Fig. 3 in which the central portion is made reentrant. At the outer point I of the reentrant air the edge is almost placed in the direction of the lines of force so that a. weak airgap does not oc out at any point; also in this arrangement the lines of force flow nearly parallel at the edge and are gradually reduced with respect to their number.

In order to completely avoid residual air between the solid dielectric and the plate, the surfaces of the insulation abutting the condenser plates :1 are preferably coated with a metallic layer free of air in any known manner and this to the invention, in which the plates are likewise designated a while the intermediate layers of insulation are denoted b. The metallic plates are laterally extended for the purpose of improving the possibilities for cooling the condenser. It will easily be observed that very large metallic cooling surfaces are obtained also at the edge of the condenser assembly according to my present invention in contradiction to the heretofore known constructions in which the ceramic insulation is generally provided at its edge with a thick extension which cannot be coated with metal. Its capability of heat conduction to the surrounding air is consequently considerably reduced.

When using intermediate dielectric members as shown in Fig. 3, the thickness of these members is preferably slightly reduced at the edge indicated by r so as to protect this weak outer part of the insulation against damages when pressure becomes applied during the mounting operation.

The Fig. 6 shows a top view of the condenser assembly. The individual elements of such assembly are fixed in a customary clamping device m, n, o and p. The insulation at the ends of this assembly consists of a plurality of standard insulation layers b. These intermediate layers are shown as circular members since this shape is the most convenient. It is obvious that a condenser assembly of this type involving superior possibilities for cooling can be subjected to a much higher load than the customary condenser assemblies having insulating members with an enlarged edge or rim. The individual elements may also after finished mounting to its desired shape be connected either in series or in parallel to one another so that the condenser assembly is applicable to a very wide frequency and potential range. l

The use of the above described condenser assembly for direct voltages involves the advantage that the electric field at the edge of the intermediate insulation is defined by the field formed between the condenser plates a but not by accidental changes in the surface of the insulation having their origin in different mechanical strengths. The possibilites for flashing-over are therefore considerably reduced.

The condensers are assembled in generally the same manner as is customary in the production of mica condensers of the pile type. For the purpose of securing alignment of the intermediate layers, the assembly jig may, for instance, be provided with four vertical rods In projecting through holes 2 in the electrode plates. After each plate has been placed in its correct position the washers l are arranged between the plates which maintain the latter in their relative positions when the intermediate insulating member I is placed in its position. It is obvious that slots may replace the holes i. It is important that the holes or slots are sufficiently spaced from the area of the intermediate layer so that the lines of force having their origin at the edge of the holes will not be increased on account of the high dielectric constant of the intermediate layer.

The particular advantages involved due to the above described new construction of a condenser consist in the fact that materials having a very high dielectric constant may be used as intermediate insulating members without introducin the disadvantage of a field concentration. The space requirements are therefore considerably decreased and the possibilities for cooling are far better due to the projecting condenser plates than in the heretofore known devices. When intended for the same operating conditions, a condenser according to my present invention is smaller and therefore considerably reduced with respect to its costs.

If desired the novel type of condenser above described in connection with Fig. 6 may be oil impregnated in accordance with a further feature of my invention.

What is claimed is:

l. A condenser device comprising two interme diate solid dielectric members of equal shape but composed of materials having different temperature coefficients, the parallel major surface of each of said members being covered with a metallic coating and the outer edge of said combined members beinggradually bevelled toward its outer boundary, and a pair of metal condenser plates extending outwardly beyond the outer boundary of said combined members.

2. A condenser device comprising a solid dielectric member having a central portion bounded by parallel major surfaces and an outer peripheral portion, said outer peripheral portion being cut down at substantially a right angle with respect to said parallel major surfaces, at a place adjacent said major surfaces, and the remainder of said peripheral portion being gradually beveled down toward its outer boundary, a pair of metallic coatings intimately covering said major surfaces so as to eliminate residual air between said coatings and said surfaces, and a pair of metaicondenser plates covering said coatings and extending outwardly so as to overlie at least the greater part of said beveled outer peripheral portion.

3. A condenser device comprising a solid dielectric member havinga central portion bounded by substantially parallel major surfaces and an outer peripheral portion beveled toward its outer boundary, said outer peripheral portion ad- Jacent said major surfaces being cut down at substantially a right angle with respect to said major surfaces and the remainder of said peripheral portion being gradually beveled down toward its outer boundary, and a pair of metal condenser plates against said major surfaces and extending outwardly so as to overlie a substantial part of said beveled outer peripheral portion.

4. A condenser device comprising two intermediate solid dielectric members of equal shape and composed of materials having dilferent temperature coefficients. said members having surfaces abutting in contact with eacl other and having outer parallel major surfaces, 1 be outer peripheral edge of the abutting members gieing gradually beveled toward the outer boundary, and a conducting. condenser plate adjacent each major surface and extending outwardly beyond the boundary of said abutting members.

HERMANN GGNNINGEN. 

